This invention is directed generally to stabilized polysilylenes, and more specifically to processes for the photostabilization of polysilylene polymers by utilization of stabilizer additive components. More specifically, in one embodiment the present invention is directed to the incorporation of stabilizers into polysilylenes, particularly UV stabilizers for the primary purpose of preventing degradation of the polysilylene upon exposure to light, and the selection of the resulting stabilized material in a layered photoresponsive imaging members. The aforementioned members in one particular aspect of the present invention are comprised of a supporting substrate, a photogenerating layer, and in contact therewith, a hole transport layer comprised of a stabilized polysilylene, especially poly(methylphenyl silylene), poly(n-propyl methyl silylene), and other similar silylenes. Additionally, the layer with the stabilized polysilylene hole transporting compound can be located as the top layer of the imaging member, or alternatively it may be situated between the supporting substrate and the photogenerating layer. In addition, the aforementioned members are particularly useful in electrophotographic, and especially xerographic imaging processes including those wherein there are selected for development liquid ink compositions.
Imaging members comprised of polysilylenes are illustrated in U.S. Pat. No. 4,618,551, the disclosure of which is totally incorporated herein be reference. More specifically, there is illustrated in this patent a polysilylene hole transporting compound for use in layered imaging members comprised of the formula as recited in claim 1, for example. More specifically, there is described in the aforementioned patent an improved layered photoresponsive imaging member comprised of a supporting substrate, a photogenerating layer, and as a hole transport layer in contact therewith, a polysilylene compound of the formula ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently selected from the group consisting of alkyl, aryl, substituted alkyl, substituted aryl, and alkoxy; and m, n, and p are numbers that reflect the percentage of the particular monomer unit in the total polymer compound. Preferred polysilylene hole transporting compounds illustrated in this patent include poly(methylphenyl silylenes), which silylenes more preferably have a weight average molecular weight of in excess of 50,000, and preferably are of a weight average molecular weight of about 75,000 to about 1,000,000. The aformentioned polysilylenes can be prepared by known methods, reference the Journal of Organometallic Chemistry, page 198, C27, (1980), R. E. Trujillo, the disclosure of which it totally incorporated herein by reference. Also, other polysilylenes can be prepared as described in the Journal of Polymer Science, Polymer Chemistry Edition, Vol. 22, pages 225 to 238, (1984), John Wiley and Sons, Inc., the disclosure of which is totally incorporated herein by reference. More specifically, the aforementioned polysilylenes can be prepared as disclosed in this article by the condensation of a dichloromethyl phenyl silane with an alkali metal such as sodium. In one preparation sequence, there is reacted a dichloromethyl phenyl silane in an amount of from about 0.1 mole with sodium metal in the presence of 200 milliliters of solvent, and wherein the reaction is accomplished at a temperature of from about 100.degree. C. to about 140.degree. C. There results, as identified by elemental analysis, infrared spectroscopy, UV spectroscopy, and nuclear magnetic resonance, the polysilylene products subsequent to the separation thereof from the reaction mixture.
When selecting components for photoreceptors, particularly photogenerating or hole transport substances, it is important that when the member is exposed to light that it retain its stability; and more specifically, that the components thereof are not adversely effected by light causing them to degrade or decompose and thereby rendering them substantially useless for their intended purposes. In addition, during the corona charging step in electrostatic imaging processes, the voltages emitted may cause degradation of the components in the imaging member affecting the undesirable degradation thereof, and permitting emission of products, and in some instances, hazardous products to the environment. The aforementioned polysilylenes may, after some usage, degrade upon exposure to light, or may emit undesirable products subsequent to the corona charging step causing both changes in the electrical, that is transporting properties of the polysilylenes, and the mechanical characteristics thereof thereby rendering them substantially unsuitable in some instances for untilization in electrostatographic photoreceptors. Accordingly, there is a need for processes that will permit the stabilization of the aforementioned polysilylenes to enable their incorporation into photoconductive imaging members thereby preventing degradation thereof, and enabling the resulting members to be useful for extended time periods exceeding, for example, 1,000,000 imaging cycles without degradation. This is accomplished in accordance with the present invention by affecting stabilization of the polysilylenes.
Prior art patents of background interest which teach the degradation of polysilylenes by ultraviolet light include, for example, U.S. Pat. Nos. 4,464,460; 4,587,205; and 4,588,801. Also of interest is U.S. Pat. No. 4,172,933, which illustrates the introduction of an active compound into a transport polymer as a pendant moiety, reference columns 3 and 4 thereof.